State health officials warned residents this week to take extra precautions against mosquito bites, noting that two species that can carry infectious diseases such as dengue fever, chikungunya and yellow fever have been found in the Southland.

“While the risk is still low in California, infected travelers coming back to California can transmit these viruses to mosquitoes that bite them,” state public health officer Dr. Karen Smith said. “This can lead to additional people becoming infected if they are then bitten by those mosquitoes.”

State health officials said the mosquito species Aedes albopictus was detected in September in San Diego and Kern counties, and it has expanded in parts of Los Angeles County. Also last month, the mosquito Aedes aegypti was detected in Riverside and San Bernardino counties. That species was first detected in California in 2013, and was then spotted in 10 counties, including Los Angeles, Orange and San Diego. Neither species is native to California. They are known for their black- and-white stripes, biting during the middle of the day and readily entering buildings.

“There is no vaccine or treatment for chikungunya or dengue fever,” Smith said. “To prevent these diseases from becoming established in California, it is important for everyone to take steps to keep these mosquitoes from spreading.”

She asked residents who spot the mosquitoes to contact a local vector control agency. Residents were advised to use mosquito repellents containing DEET, picardin, IR3535 or oil of lemon eucalyptus; wear long-sleeve shirts, long pants, socks and shoes when mosquitoes are most active; ensure home windows and door screens are intact to keep mosquitoes out; and eliminate breeding sources, such as water-filled containers and water that collects at the bottom of potted plants, in bird baths and discarded tires.